voxl-mavlink-server

Table of contents

1. Overview
2. Configuration
   1. udp_mtu
3. Pipes
   1. rc_active source selection

Overview

voxl-mavlink-server manages MAVLink routing between network interfaces, MPA applications, and the flight controller such as PX4.

Configuration

voxl-mavlink-server reads its configuration from /etc/modalai/voxl-mavlink-server.conf. The available fields and their defaults (as of v1.4.20) are:

Never set primary_static_gcs_ip or secondary_static_gcs_ip to localhost, these are meant for external ground control stations. For local MAVSDK and MAVROS communication, set the en_localhost_mavlink_udp flag in voxl-vision-hub’s /etc/modalai/voxl-vision-hub.conf file instead.

udp_mtu

For radios, such as Doodle Labs, that utilize larger packet sizes with increased latency, voxl-mavlink-server can bundle mavlink messages headed to the GCS into larger UDP packets. Since v1.4.14 this aggregation is on by default with a udp_mtu of 512 bytes. Set udp_mtu to 0 to disable aggregation and send one UDP packet per message. The config file contains the following description of the field:

 * udp_mtu - maximum transfer unit for UDP packets back to GCS. voxl-mavlink-server
 *           will bundle up backets for the GCS into a single UDP packet with 
 *           a maxium size of this. This saves network traffic drastically.
 *           Set to 0 to disable this feature and send one UDP packet per msg.

Try a few different values such as 100, 200, 300 etc to find an optimal value for your setup.

Pipes

voxl-mavlink-server publishes the following 14 pipes into MPA.

Data from the high-rate onboard stream:

• mavlink_onboard: full high-rate ‘onboard mode’ mavlink stream from the autopilot
• mavlink_ap_heartbeat: autopilot heartbeat messages
• mavlink_sys_status: sys_status messages
• mavlink_gps_raw_int: gps_raw_int messages
• mavlink_attitude: attitude messages
• mavlink_local_position_ned: local_position_ned messages
• imu_mavlink: IMU data from the autopilot
• px4_baro: barometer data from the autopilot
• rc_channels: RC channel data
• rc_active: active RC source, muxing rc_channels, manual_control and (v1.4.20 and newer) RC_CHANNELS_OVERRIDE. See rc_active source selection.

GCS-related pipes:

• mavlink_to_gcs: normal-rate stream from the autopilot to the GCS
• mavlink_from_gcs: data coming from the GCS
• gcs_ip_list: list of IP addresses of connected GCS
• mission: mission data

Up to 16 simultaneous GCS connections can be established over UDP port 14550. See the Mavlink Routing feature guide for the routing paths and how to inspect these pipes with voxl-inspect-mavlink.

rc_active source selection

The rc_active pipe publishes RC from one source at a time:

• MANUAL_CONTROL from a GCS joystick, and RC_CHANNELS_OVERRIDE from a GCS or from an onboard application writing to the control channel of the mavlink_onboard pipe, are both RC arriving over IP and share one priority tier. RC_CHANNELS_OVERRIDE needs v1.4.20 or newer.
• RC_CHANNELS_OVERRIDE channels pass through unchanged, up to 18 channels.
• An over-IP source stays fresh for 5 s after the last MANUAL_CONTROL message and 1 s after the last RC_CHANNELS_OVERRIDE message.
• Whichever over-IP source is active keeps the pipe while it stays fresh, so two senders never interleave. The other source takes over once the active one goes stale.
• With en_elrs_rc_mux set, a live ELRS link outranks both over-IP sources. If no source is available the pipe publishes nothing instead of stale failsafe values.
• Without en_elrs_rc_mux, rc_channels is used when neither over-IP source is fresh.
• manual_control_active is 1 when the published data is RC over IP (MANUAL_CONTROL or RC_CHANNELS_OVERRIDE).